A navigation system, such as the global navigation satellite system (GNSS), provides location and time information with line-of-sight (LOS) to four or more navigation satellites. Although four satellites are required for normal operation, fewer are possible in cases where one variable, e.g., elevation is known or irrelevant. The navigation system provides positioning services to a moving vehicle by tracking the satellite signals during the movement of the vehicle. However, the navigation system of the vehicle can lose one or more satellite signals when the LOS with the satellite transmitting the satellite signal is occluded by environmental features, such as trees, buildings, or bridges. After the tracking of the satellite signal is lost, the satellite signal must be reacquired when the LOS with the satellite is restored. The reacquisition of the satellite signal is a time consuming process, because the frequency and phase of the satellite signal to be tracked are varying in response to a change in relative positions and/or velocities between the moving vehicle and the transmitting satellite, and are usually unknown.
Some navigation systems use temporal and spatial diversity to minimize problems with LOS occlusion. For example, the system and method described in U.S. Pat. No. 7,642,957 uses two antennas to receive satellite signal with the expectation that at least one antenna receives a “good” signal. Another system sets up a local constellation, as in U.S. Pat. No. 5,886,665, where dedicated transceivers with known locations rebroadcast the satellite signals into areas with a “poor” signal. However, such a system is expensive to install and maintain and requires dedicated and protected real estate to operate.
If a vehicle is moving at a high speed through an environment littered with features that could occlude the satellite signals, it is possible that the signals can only be received for a time that is shorter than the required acquisition time.
Accordingly, there is a need for a method that speeds up the acquisition time of satellites signals by a navigation system of the moving vehicles.